The present invention relates generally to systems and methods for suppressing machinery fires, and more particularly to an economical, lightweight and reliable structure for mitigating the ignition of a flammable fluid leaked from the machinery onto a hot surface.
Powdered machinery may operate at very high exterior temperatures as a result of internal combustion or electrical power, grinding or machinery operations, friction or other causes that characterize the operation. In particular, surfaces near the combustion region, exhaust manifolds, or bleed air/steam ducts of an operating engine can reach extremely high temperatures. Flammable fluids such as fuel, oil or hydraulic fluid in use near such surfaces leaking onto the hot surfaces and igniting has been documented as a frequent cause of fires near hot operating machinery, especially in automobiles. Aboard aircraft, a common cause of engine fires is the leakage of such fluids in the engine nacelle and subsequent ignition of the fluid by the hot engine core or uninsulated bleed air ducts. On-board fire extinguisher systems may be rendered ineffective if the fire is re-ignited by the hot surface after the extinguishant is depleted.
The invention solves or substantially reduces in critical importance problems in the prior art by providing a platform, housing, conduit, exhaust duct or other structural element that encloses or supports an engine (or other hot operating machinery) and which are heated in the course of engine operation, for mitigating ignition of flammable liquids that come into contact with such heated structure. A pattern of micro-cavities is defined on the outer surface of the structure and sized to minimize flammable liquid seepage into the cavities because of surface tension of the liquid, thereby preventing wetting of the interior of the cavities by the liquid. A gridwork of the cavities on the surface of the structure may provide 50% or more reduction of direct surface to liquid contact when the liquid spreads across the surface, which minimizes heat transfer to an vaporization and ignition of the liquid. The cavities also promote formation of nucleate bubbles at the onset of boiling that percolate harmlessly through the liquid, rather than form a superheated vapor film beneath the liquid that could seep from under the liquid pool, mix with air and ignite. The cavity pattern may be formed in the structure surface by machining, stamping, rolling, casting or other conventional process. The invention allows substantially hotter operating surface temperatures for the engine, or delays ignition of flammable liquids contacting the structure, and thereby allows a wider range of operating temperatures for the engine safe from the risk of fire. The invention adds no weight to the machinery, is highly reliable and adds no operating cost after initial fabrication. The invention may be conveniently incorporated into bleed air ducts and engine surfaces of aircraft engines and auxiliary power units, military ground vehicle and ship engine or other machinery compartments, commercial vehicles, marine vessels, ground support and stationary power equipment and other industrial machinery applications where liquid-fueled, oiled or hydraulically controlled equipment is operated near hot components of operating machinery.
It is therefore a principal object of the invention to provide structure and method for suppressing machinery fires.
It is another object of the invention to provide a novel structure for a platform, housing, conduit or other structural form for a hot operating engine, machinery or other hot component.
It is another object of the invention to provide a novel structure for a platform, housing, conduit or other structural form that enclose or support a hot operating engine, machinery or hot component and which mitigate the ignition of flammable liquids contacting the structure.
It is a further object of the invention to provide an inexpensive, maintenance free system for suppressing fires near hot operating machinery.
It is a further object of the invention to provide a means of preventing fires near hot structures without adding additional weight to the structure.
It is a further object of the invention to provide a means to mitigate hot surface-induced ignition of fluids without reducing the ability of the hot structure to expel excess heat under normal operating conditions.
These and other objects of the invention will become apparent as a detailed description of representative embodiments proceeds.